Comprehensive Study Guide: NSW Year 10 Science (Reactions and Sustainability)

Focus Area 1: Law of Conservation of Mass

• The Law of Conservation of Mass: This is an unbreakable law of the universe stating that matter can neither be created nor destroyed in a chemical reaction.

• Total Mass Equality: In a closed system, the total mass of the reactants before a chemical reaction must equal the total mass of the products after the reaction.

• Atomic Rearrangement: During a chemical change, atoms in the reactants are rearranged to form new substances. The number of each type of atom remains identical on both sides of the reaction.     * Example: Electrolysis of Water: Two water molecules can be broken apart. The covalent $O-H$ bonds break, and the atoms rearrange to form $H_2$ and $O_2$.

• Open vs. Closed Systems:     * Open System: Allows matter to flow in and out. Mass may appear to be lost or gained because gases escape or enter from the surroundings.         * Example: Campfire: Wood reacts with oxygen to form carbon dioxide and water vapor, which float away, making the wood appear to "disappear."     * Closed System: Matter cannot enter or leave. Substances change form, but total mass stays constant.         * Investigation Example: Silver nitrate and copper wire in a sealed flask. Copper replaces silver in the solution; despite visual changes, the flask mass remains unchanged.

• Practical Demonstration: Burning Steel Wool:     * Chemical Reaction: $4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(s)$     * Observation: The mass of steel wool ($4.0\,g$) increases after burning because it reacts with oxygen from the air to form iron(III) oxide (rust).

Focus Area 2: IUPAC Naming and Chemical Formulas

• Elements vs. Compounds:     * Element: A pure substance made of the same atom(s).     * Compound: A pure substance made of two or more different atoms.

• Classification by Properties:     * Metals: Lustrous, malleable, ductile, dense, high melting/boiling points, good conductors of heat and electricity.     * Non-metals: Dull, brittle, not ductile, low density, low melting/boiling points, poor conductors.     * Semi-metals (Metalloids): Properties of both; e.g., brittle but semi-conductors.

• Covalent Compounds:     * Bonding: Formed between non-metals/semi-metals by sharing valence electrons to achieve stable full shells.     * Naming Conventions: Add suffix "-ide" to the second element and use Greek prefixes for both.         * Prefixes: $1 = \text{mono}$, $2 = \text{di}$, $3 = \text{tri}$, $4 = \text{tetra}$, $5 = \text{penta}$, $6 = \text{hexa}$, $7 = \text{hepta}$, $8 = \text{octa}$, $9 = \text{nona}$, $10 = \text{deca}$.         * Exceptions: "Mono-" is omitted for the first element. Drop the "a" from a prefix if the element is oxygen (e.g., tetroxide).

• Ionic Compounds:     * Bonding: Formed between metals (cations) and non-metals (anions) via transfer of electrons, resulting in electrostatic attraction.     * Formula Determination: Use the "crossing over" method for valencies or ensure the total charge equals zero.     * Naming: Identify elements, add "-ide" to the second element. Use Roman numerals for transition metals with ambiguous valencies (e.g., Iron (III) oxide, $Fe_2O_3$).     * Polyatomic Ions: Groups of atoms covalently bonded with an overall charge.         * $OH^- = \text{hydroxide}$         * $SO_4^{2-} = \text{sulfate}$         * $NO_3^- = \text{nitrate}$         * $PO_4^{3-} = \text{phosphate}$         * $CO_3^{2-} = \text{carbonate}$         * $NH_4^+ = \text{ammonium}$

Chemical Equations and Balancing

• Chemical Equations: Describe changes during a reaction using standard symbols: $\text{Reactants} \rightarrow \text{Products}$.

• State Symbols:     * $(s)$ = solid     * $(l)$ = liquid     * $(g)$ = gas     * $(aq)$ = aqueous (dissolved in water)

• Balancing Rules:     1. Never change the subscripts in a chemical formula.     2. Adjust the coefficients (numbers in front) to ensure the same number of atoms for each element on both sides.

• Diatomic Molecules: Certain elements occur naturally as pairs: $H_2$, $N_2$, $O_2$, $F_2$, $Cl_2$, $Br_2$, $I_2$.

Energy in Chemical Reactions

• Bond Energy Balance:     * Bond Breaking: Requires energy input.     * Bond Formation: Releases energy.

• Exothermic Reactions: Release energy (usually heat). Occurs when the energy released forming new, stronger bonds is greater than the energy used to break original, weaker bonds.     * Example: Combustion of methane ($CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$). Total reactant energy is $634\,kcal/mol$; product energy is $804\,kcal/mol$. Net release: $170\,kcal/mol$.

• Endothermic Reactions: Absorb energy. More energy is required to break reactant bonds than is released in product formation.

Types of Chemical Reactions

• Synthesis (Direct Combination): Multiple reactants combine to form one complex product ($A + B \rightarrow AB$).     * Example (Corrosion): $4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(s)$.

• Decomposition: A single compound breaks down into simpler substances ($AB \rightarrow A + B$). Requires energy (heat, light, electricity).     * Photolysis: $2AgCl(s) \xrightarrow{\text{UV Light}} 2Ag(s) + Cl_2(g)$.     * Thermal Decomposition: $CaCO_3(s) \xrightarrow{\text{Heat}} CaO(s) + CO_2(g)$.

• Displacement Reactions:     * Single Displacement: A more reactive metal replaces a less reactive metal in a compound ($A + BC \rightarrow AC + B$).         * Reactivity Series: Metals like $Mg$ and $Zn$ are higher and can displace $Cu$ from $CuSO_4$.     * Double Displacement: Ions of two ionic compounds exchange places ($AB + CD \rightarrow AD + CB$).         * Precipitation: Two soluble solutions react to form an insoluble solid (precipitate). Use solubility rules (e.g., NAGSAG mnemonics) to predict products.         * Net Ionic Equations: Show only the participating ions, removing spectator ions.

• Neutralization: An acid reacts with a base to form salt and water ($\text{Acid} + \text{Base} \rightarrow \text{Salt} + H_2O(l)$).

Focus Area 3: Rates of Reaction and Collision Theory

• Collision Theory: States that a reaction rate depends on the frequency of effective collisions. For a collision to be effective:     1. Particles must collide with the correct orientation.     2. Particles must have sufficient kinetic energy to overcome the Activation Energy ($E_a$) barrier.

• Factors Affecting Reaction Rate:     1. Surface Area: Increasing surface area (crushing solids) increases the interface for contact, leading to more frequent collisions.     2. Concentration: Higher concentration increases the number of particles per unit volume ($dm^3$), increasing collision frequency.     3. Temperature: Increases the average kinetic energy. Particles move faster (more frequent collisions) and a larger proportion of particles have energy $> E_a$.     4. Catalysts: Speed up reactions by providing an alternative pathway with a lower Activation Energy, making effective collisions more frequent. They are not consumed.     5. Stirring: Physically moves particles, increasing movement and collision frequency.

• Measuring Reaction Rates:     * Gas Production: Measured via upturned measuring cylinder (water displacement) or gas syringe ($cm^3/s$).     * Mass Loss: Measured via electronic balance as gas escapes ($g/s$).     * Solid Production: Measured by the time taken for a cross under the flask to disappear due to precipitate formation.

Focus Area 4: Nuclear Reactions

• The Big Bang Theory: The universe began as a singularity approximately $13.7 \times 10^9$ years ago and expanded rapidly.     * Timeline: Quarks formed $\rightarrow$ protons/neutrons $\rightarrow$ nuclei of $H$, $He$, $Li$ (first minutes) $\rightarrow$ first atoms (after $370,000$ years).     * Evidence for Expansion:         * Red Shift: Wavelengths from distant galaxies appear longer, indicating they are moving away.         * Cosmic Microwave Background Radiation (CMBR): The "afterglow" radiation from the early universe.

• Nucleosynthesis: Heavier elements formed inside stars (Fusion) or during Supernovae.

• Atomic Structure:     * Atomic Number ($Z$): Number of protons.     * Mass Number ($A$): Protons + Neutrons.     * Isotopes: Atoms of the same element with different numbers of neutrons.

• Radioactive Decay: Spontaneous emission of radiation by unstable nuclei.     * Alpha (⍺): Helium nucleus ($2\,protons$, $2\,neutrons$). Low penetration, high ionization.     * Beta (β-): Fast-moving electron. Medium penetration and ionization.     * Gamma (ᵞ): High-energy photons (EMR). High penetration, low ionization.

• Half-Life: The time required for half of the initial radioactive nuclei in a sample to decay.

• Nuclear Fission vs. Fusion:     * Fission: Splitting a heavy nucleus ($U-235$) into lighter ones ($Ba$, $Kr$) using neutrons. Used in power plants. Relies on chain reactions controlled by control rods (Boron, Cadmium).     * Fusion: Joining light nuclei (Deuterium and Tritium) to form a heavier one (Helium). Powers the sun; requires extreme heat/pressure.

Environmental Sustainability

• Sustainability Definition: Meeting the needs of the present without compromising future generations' ability to meet their own (Brundtland Commission, 1987).

• UN Principles (The 5 Ps): People, Planet, Prosperity, Peace, Partnership.

• Weather vs. Climate:     * Weather: Short-term atmospheric conditions (minutes to days).     * Climate: Long-term average pattern of weather in a region (usually $30\,years$+).

• The Greenhouse Effect:     * Natural: Necessary gases (CO2, CH4, N2O, O3) trap heat to keep Earth habitable (Avg temp $15^{\circ}C$ instead of $-18^{\circ}C$).     * Enhanced: Human activity (fossil fuel combustion) increases gas levels, trapping excess heat and causing global warming.

• Ocean Acidification: Excess CO2 absorbed by oceans lowers pH (from $8.2$ to $8.1$). This impairs calcification in shellfish, causing thinner, weaker shells.

• Waste Hierarchy: Refuse $\rightarrow$ Reduce $\rightarrow$ Reuse $\rightarrow$ Recycle $\rightarrow$ Recover $\rightarrow$ Dispose.

• Innovations:     * Plastivores: Mealworms/microbes that break down polystyrene.     * Veena Sahajwalla: Invented Green Steel and Green Ceramics (turning old clothes into kitchen tiles).

Questions & Discussion

• Q: Why does conducting reactions in a closed system give more accurate evidence for the law of conservation of mass?     * A: It prevents matter (like gas products) from escaping or entering, ensuring all mass is accounted for.

• Q: When magnesium burns in air, why does the mass increase?     * A: Because the magnesium atoms bond with oxygen atoms from the atmosphere, adding the mass of the oxygen to the solid product (Magnesium Oxide).

• Q: Joy says water mass decreased relative to volume in a glass; Paul says it evaporated into the air. Who is correct?     * A: Paul is correct. Matter is conserved; it moved from the liquid phase to the gas phase in the air, rather than being destroyed.

• Q: Why are catalytic converters less efficient when a car starts cold?     * A: Catalysts and the reactions they facilitate are temperature-dependent. At low temperatures, the particles have less kinetic energy, leading to a slower rate of reaction within the converter.

• Q: Why is "shrinking the hallways" a good analogy for concentration?     * A: It reduces the volume available, forcing particles closer together and increasing the frequency of collisions.